As one of directional control valves, a three position directional control valve, which performs switching control for fluid supply in three directions (a fluid supply position in a forward direction, a supply suspension position, and a fluid supply position in a backward direction), is publicly known. As this type of directional control valves, there is one which merely performs three ON/OFF position switching, however, there is also one which performs proportional control of amount of supplying fluid in response to amount of a spool stroke from the supply suspension position (a neutral position). Regarded to this proportional control concerned, in addition to direct control valve by manual, there are also well-known proportionally controlled valves as using a pilot pressure or operatively controlled electric (operatively controlled electromagnetic force) (for example, refer to Patent Document 1).
FIG. 7 illustrates a system configuration of the three position directional control valve which is operatively controlled electrically. This system comprises, in addition to the three position proportional control valve 100, left and right springs 102a and 102b, and electromagnetic proportional pressure reducing valves 111 and 112 controlling pilot pressure supply to left and right ends of the spool from a pilot pressure source 115, in order to perform spool position control. The three position proportional control valve 100 switches from the neutral position (supply suspension position) 101c, to the left activated position 101a, or the right activated position 101b. In response to a position of the spool, it stops hydraulic supply to an actuator 108 by setting a position of the spool to the neutral position 101c, supplies hydraulic oil from a hydraulic pump 105 to a left oil chamber (bottom side oil chamber) of the actuator 108 and discharges the hydraulic oil of a right oil chamber (rod side oil chamber) to the tank 106 by setting to the left activated position 101a (setting the left activated position 101a to the center, illustrated as the neutral position 101c), and supplies the hydraulic oil from the hydraulic pump 105 to the right oil chamber of the actuator 108 and discharges the hydraulic oil in the left oil chamber to the tank 106 by setting the right activated position 101b. 
In order to perform position control of the three position proportional control valve 100, that is, spool position control, a command signal is transmitted to the electromagnetic pressure reducing valve 111 or 112, and pilot pressure depending on the command signal is applied on an end of the spool. For example, in order to move the spool leftward, pilot pressure is applied on the right end of the spool by the right electromagnetic proportional pressure reducing valve 112. This makes the spool pressed to stroke to leftward direction until the force generated with pilot pressure balances with the spring force of the left spring 102a so that the spool is settled on the rightward activated position 101b with the stroke corresponding to the above mentioned command signal.